Memory circuits are commonly found in many electronic devices and must obtain a continuous supply of power to retain data. Such memories are often used within battery-powered wireless products where power consumption is one of the most important design considerations. Others have implemented battery-powered wireless products with memory circuits that transition from an active mode to a sleep mode operation that consumes less power. However, as transistor dimensions shrink, the transistor current leakage increases proportionately. Transistor current leakage results from a sum of sub-threshold leakage current, gate leakage and diode leakage current. The transistor current leakage requires memories to be powered when in the sleep mode operation. To reduce current leakage during a sleep mode of operation the supply voltage may be lowered. Alternatively, the ground or low voltage may be increased to reduce the voltage differential between the high voltage terminal and the low voltage terminal. However, sufficiently lowering the high voltage or increasing the ground reference may result in an increase in diode current that becomes significant relative to savings in the gate current and the sub-threshold current. As devices are made smaller, heavier doping is required to control short channel effects. The heavier doping that is found in smaller semiconductor devices limits sub-threshold current with scaling but increases a transistor's diode leakage. The diode leakage can result in a loss of data in a low power or sleep mode of operation.
Skilled artisans appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.